While the association between obesity and cardiovascular disease is well established, the mechanisms leading to cardiovascular abnormalities in obesity remain unclear. However, there is an increasing appreciation for the possible importance of the obstructive sleep apnea syndrome (OSA). Recent data have convincingly shown that sleep apnea is causally associated with systemic hypertension. There is also some data to support a role for OSA in the development of insulin resistance, sympathetic excitation, and endothelial dysfunction. While the importance of sytemic inflammation, fibrinolytic abnormalities and dyslipidemia are well known in relationship to cardiovascular disease, the role of sleep-disordered breathing in causing abnormalities in these areas remains unexplored. Furthermore, the clear overlap between obesity and OSA make it difficult to distinguish the independent effects of one versus the other. We propose to make a thorough assessment of the independent and perhaps synergistic roles of sleep apnea and obesity in leading to abnormalities in autonomic activation, endothelial function, insulin sensitivity, serum lipids, inflammation and fibrinolysis. In doing so, our protocols will provide useful insights into the mechanisms of obesity associated cardiovascular disease, and the specific role played by sleep-disordered breathing. This data may have important implications for the diagnosis and treatment of these abnormalities.